Flower visitors on spring oilseed rape in different cropping systems
Karise, R.(Estonian Agricultural Univ., Tartu (Estonia))E-mail:[email protected] | Maend, M.(Estonian Agricultural Univ., Tartu (Estonia)) | Viik, E.(Estonian Agricultural Univ., Tartu (Estonia)) | Martin, A.J.(Estonian Agricultural Univ., Tartu (Estonia)) | Laeae, P.(Estonian Agricultural Univ., Tartu (Estonia))
Spring oilseed rape (Brassica napus var oleifera subvar. annua) is predominantly autogamous and visits of insect pollinators are not essential for the final seed yield. However, the pollinators can have positive effects, such as a reduction of the flowering period, a reduction of raceme production, acceleration of ripening and an increase of seed weight. This study considers (i) the effect of different fertilising systems on the number of flowers and the food resource in flowers of summer oilseed rape; (ii) the effect of flower number and food resources on the abundance of flower visitors. Field experiments were carried out in July 2003 to compare the density of pollinators foraging on the different cropping systems of the summer oilseed rape. The number of pollinating insects was counted twice a week on sunny days between 11:00 and 15:00 when the temperature was above 16 deg C. Flowers were counted at the same time on an area of 1 square m on each plot. The amount of nectar present in the flowers was measured by inserting a l mul capillary into the flower corrolla tube. The number of pollen grains was counted from the samples after dissolving the flower tissues. The results showed that the most important pollinators were honey bees (Apis mellifera), collecting both pollen and nectar. The rape field were less visited by wild bees, different flies, including syrphus flies (Syrphidae), and butterflies. The food resource available for flower visitors did not depend on the fertilising system. The density of bees depended only on the flower density of the field.
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